Impact of early hypocapnia on development of bronchopulmonary dysplasia in premature neonates
Introduction: There are likely multiple contributing factors to the development of bronchopulmonary dysplasia, including early ventilatory management. There has been increasing emphasis on providing gentle ventilation in the delivery room in an effort to reduce barotrauma, volutrauma and atelectotrauma. Hypocapnia could be an important marker for overventilation. This study sought to determine if, in infants <29 weeks at birth, hypocapnia during initial stabilization increases incidence of moderate/severe BPD and adverse neurological outcomes.
Methods: This is a retrospective cohort study of all inborn extremely premature (<29 weeks) infants born between 2006-2015 at the IWK Health Centre in Halifax, Nova Scotia. All pCO2 values in the first 14 days after birth were extracted. Infants were categorized as normocapnic (40-60 mm Hg), hypocapnic, hypercapnic or fluctuating for each time for their initial pCO2, first 24 hours, first seven days, and first 14 days. Frequencies of the four pCO2 categories were described, and then multivariable logistic regression was used to determine significant differences in the outcome measures for the different pCO2 categories.
Results: A total of 310 infants were included. Percentages of infants in each pCO2 category during the four prespecified time periods are shown in attached figure. The number of infants in the hypocapnic category increased between the initial pCO2 and the first 24 hours (51 to 165, p<0.001), and remained significantly increased over the first seven days compared to initial (51 to 95, p<0.001). We were unable to demonstrate an independent association of early hypocapnia with BPD, IVH or PVL.
Conclusion: Despite the majority of extremely preterm infants having a normal initial pCO2, the trend over the first 24 hours of life shows that a significant proportion of them become hypocapnic, suggesting possible overventilation in this critical early time period.